1. Field of the Invention
The present invention generally relates to a wire bonding apparatus, and more particularly to a wire bonding apparatus which is improved so as to be capable of reducing a sudden heat expansion of an IC (Integrated Circuit) lead frame. The present invention also relates to a wire bonding method which is improved so as to be capable of reducing a sudden heat expansion of an IC lead frame.
2. Description of the Background Art
FIG. 5 is a plan view of a bonding part of a semiconductor device.
Referring to FIG. 5, there is hitherto a step of mounting an IC chip 1 on an IC lead frame and connecting a bonding pad 2 on the IC chip 1 and an inner lead 4 of the IC lead frame with the use of a metal fine wire 5 to establish an electrical connection between the IC chip 1 and the inner lead 4. At that time, the IC chip 1 on a die pad 3 and the inner lead 4 on the IC lead frame are heated with a heater to carry out wire bonding. This step is carried out in a wire bonding apparatus.
FIGS. 6A and 6B are views schematically illustrating a platen used in a conventional wire bonding apparatus. FIG. 6A is a plan view and FIG. 6B is a cross section view. FIG. 7A is a plan view illustrating the manner in which an IC lead frame is heated with a platen, and FIG. 7B is a cross section view thereof. FIG. 8 is a plan view of an IC lead frame.
Referring to these drawings, a conventional wire bonding apparatus includes a heat block 16. A platen 6 that accords with the shape of an IC lead frame 7 is disposed on the heat block 16. Die pads 22a, 22b are disposed on the IC lead frame 7. A bonding point 2a is disposed in the platen 6. Only an IC chip mounted on the die pad 22a and an inner lead 4 of a corresponding IC lead frame, which are at a bonding position 18 on the platen 6, are heated.
This method generates an inconvenience such that, particularly in the case where the material of the IC lead frame 7 is copper, the IC lead frame 7 expands by heat to cause variations in the die pad position at the time of wire bonding. Variations in the die pad position cause variations in the position of the IC chip mounted on the die pad as well. Therefore, with the position of the IC chip shifted, the bonding pad of the IC chip and the inner lead of the IC lead frame are connected with a metal fine wire, thereby raising a problem in that the metal fine wire is not connected at a normal position on the bonding pad of the IC chip.
The present invention has been made in order to solve the aforesaid problem, and an object thereof is to provide a wire bonding apparatus which is improved so that the metal fine wire is connected at a normal position on the bonding pad of the IC chip.
Another object of the present invention is to provide a wire bonding method which is improved so that the metal fine wire is connected at a normal position on the bonding pad of the IC chip.
The invention according to the first aspect of the present invention is directed to a wire bonding apparatus for connecting an inner lead of an IC lead frame and an IC chip mounted on the IC lead frame with a metal fine wire. The wire bonding apparatus includes a heat block that heats the IC chip and the IC lead frame. A platen is disposed on the heat block in accordance with a shape of the IC lead frame for enlarging a heat transfer surface. A heating part for heating the IC chip and a preheating part for preheating an IC chip that is to be heated next are disposed on a surface of the platen.
According to this invention, an IC chip and an inner lead that are located prior to the bonding position by one pitch can be heated in the same manner as an IC chip and an inner lead that are located at the bonding position, thereby allowing the heat expansion of the IC lead frame to be saturated before bonding. Therefore, there will be no variations in the positions of the die pad and the IC chip at the time of bonding. As a result, the metal fine wire can be bonded at a normal position on the bonding pad of the IC chip.
In a wire bonding apparatus according to the second aspect of the present invention, a height of a surface of the preheating part is selected so that a gap between the IC lead frame and the preheating part will be from 0 to 1 mm.
According to this invention, sudden heating of the IC lead frame can be prevented.
In a wire bonding apparatus according to the third aspect of the present invention, the preheating part is constructed to be separable from the platen.
According to this invention, the preheating part can be replaced with a variety of other preheating parts, so that the gap between the IC lead frame and the preheating part can be changed in various ways.
In a wire bonding apparatus according to the fourth aspect of the present invention, a height of the preheating part is selected so that a gap between the IC lead frame and the preheating part will be within a range from 0 to 1 mm.
According to this invention, sudden heating of the IC lead frame can be prevented.
In a wire bonding apparatus according to the fifth aspect of the present invention, the preheating part is made adjustable so that a height of a gap between the IC lead frame and the preheating part will change within a range from 0 to 1 mm in the wire bonding apparatus according to the fourth aspect.
According to this invention, sudden heating of the IC lead frame can be prevented.
A method according to the sixth aspect of the present invention is directed to a wire bonding method for connecting an inner lead of an IC lead frame and an IC chip mounted on the IC lead frame with a metal fine wire. First, an IC lead frame and an IC chip are connected with a metal fine wire while heating the IC chip (first step). Simultaneously with heating the IC chip, an IC chip that is to be heated next is preheated (second step).
According to this invention, since the IC chip which is to be heated next is preheated, the heat expansion of the IC lead frame can be saturated before bonding. Therefore, there will be no variations in the positions of the die pad and the IC chip at the time of bonding. As a result, the metal fine wire can be bonded at a normal position on the bonding pad of the IC chip.
In the method according to the seventh aspect of the present invention, the heating in the second step is carried out with a weaker power than the heating in the first step.
According to this invention, sudden heating of the IC lead frame can be prevented. In particular, oxidation of the IC lead frame can be restrained.
The foregoing and other objects, features, aspects and advantages of the present invention will becomes more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.